This invention relates to tracheostomy tube assemblies and ventilation systems.
Ventilation of a patient's lungs may be carried out either by conventional low-frequency ventilation or by high-frequency jet-ventilation. Conventional low-frequency ventilation is carried out usually by means of a cuffed endotracheal tube that has one end inserted within the patient's trachea via his mouth, or by means of a cuffed tracheostomy tube which is inserted via an incision made in the patient s throat. The cuff on the tube is inflated to form a seal between the outer surface of the tube and the wall of the trachea. Gas is supplied along the tube from a ventilating machine to inflate the patient's lungs with a suitable mixture of gases which may include an anaesthetic gas, at a rate of one pulse every several seconds.
High frequency jet-ventilation (such as described in British patent specification GB No. 1 447 987A) makes use of a smaller diameter tube located in the patient's trachea caudally of the vocal chords. Gas is administered by means of short pulses, typically one to ten pulses every second, to produce a jet within the trachea. The action of the jet causes entrainment of gas along the trachea, the combined effect producing ventilation of the patient's lungs. The jet tube can be located via the patient's mouth, nose or through an incision in his throat.
If surgery is being carried out on the upper part of the trachea, it can be a disadvantage to locate the jet tube through the nose or mouth since the tube will provide an obstruction to the surgery. A further disadvantage of previous arrangements is that, because the jet tube opens within the trachea, the expansion of gas as it emerges from the tube causes a cooling effect in the region of the tip of the tube. This can cause damage to adjacent tissue. Locating the tip of the jet tube within the trachea causes entrainment of gas within the trachea which will be a mixture of expiratory gas and fresh gas, thereby having a reduced oxygen content. Such arrangements also make it more difficult to analyze gas flows and monitor the quality of gas administered to the patient.